This invention relates to dental or prophylaxis angles, and, in particular, to a disposable dental angle and method of assembly.
Dental angles carry dental bits such as prophy cups and brushes and burs. The angle enables dentists to reach more easily the various surfaces of a patient's teeth and thus facilitates the cleaning of the teeth. These angles generally include a body having a head thereon which has a major axis angled relative to the major axis of the body. The angle is commonly 90.degree.. A drive gear and a driven gear are carried in the body in a meshing relationship. The driven gear carries a desired dental bit, such as a cleaning cup or a brush, which is to be used during the cleaning procedure. The body is slipped over the nose of a handpiece such as a Doriot type handpiece having a collet which receives the shaft of the drive gear. The collet holds the shaft, hence the angle, against axial movement. It also connects the drive gear to a motor, to rotate the drive gear, and thus the dental bit.
The use of disposable dental angles reduces the labor, cost, and risks of sterilization.
Contra-angles are often used by dental personnel for getting to difficult spots. They are generally used in conjunction with burrs, but they may also be used with prophy cups. Contra-angles include a head which is angled at a greater angle than the usual 90.degree. with respect to the axis of the handpiece. Typically the head is angled 10.degree. to 30.degree., often 15.degree. to 22.degree., from normal to the handpiece axis. In some designs, the body of the angle includes a 15.degree.-22.degree. angle formed in it; in others, an angled adapter is provided between the angle and the handpiece. To drive the dental bit secured to the head, contra-angles generally have two drive shafts. A first drive shaft extends from the bend to the Doriot to be grasped by the Doriot handpiece collet. It includes a gear at its forward end. A second drive shaft extends from the bend to the head. It includes a gear at its back end which meshes with the drive gear of the first shaft and a gear at its front end, which meshes with the gear at the end of the dental bit shaft to drive the dental bit. Contra-angles are therefore complex, expensive, and made of expensive materials. No satisfactory disposable contra-angle is presently known.
A first type of prior art disposable dental angle includes a two-piece body and is formed as a sandwich. The gears are placed in the first half of the body. The second half is then placed on top of the first half and the body is then joined such as by ultrasonic welding. However, when this type of dental angle is fitted over a collet of a Doriot handpiece, the forces exerted by the collet on the body tend to separate the body along its seams. Further, to avoid the possibility of welding the gears to the body when welding the body, the gears must fit loosely in the body. This leads to a loose fit between the gears and thus the gears do not run very smoothly.
A second type of prior art disposable angle includes a one-piece body which receives the drive gear from its rear such as is shown and described in U.S. Pat. No. 3,727,313 to Graham. A latch snaps in place behind a shoulder on the drive gear to lock the drive gear in place. However, the latch has a tendency to unhitch, allowing the drive gear to move axially within the body and to come out of contact with the driven gear. This frees the driven gear, allowing it to fall out of the head. This will cause obvious problems, especially if the latch comes undone during a cleaning procedure. The driven gear is positioned between the drive gear, and the head is thus held in place by the drive gear. Because the driven gear is placed below the drive gear, rather than above it, the dental bit rotates in an opposite direction from most other dental bits. This creates problems for hygienists who are accustomed to these other angles. During operation, the dental bit tends to "walk" due to the rotational contact with the tooth. A hygienist who has learned to compensate for "walk" in one direction, will have to become accustomed to compensating for "walk" in the opposite direction. There is, therefore, a "learning period" associated with this type of angle.
With either type of angle, the drive gear, particularly its shaft at the point where it narrows to its constant diameter, tends to overheat and fail.